1. Field of the Invention
The present invention relates to a block error detector, and more particularly, to a detector for detecting an error in a storing position of a block data used, for example, in digital video data.
2. Description of the Prior Art
Data blocks B0, B1, B3, . . . such as that shown in FIG. 1 represent a recording pattern for recording digital data, such as digital video data. Each block is composed of a number of sub-blocks, each sub-block carrying different information. The first sub-block, at the very beginning of the block carries a sync data of two words long (one word is eight bit long). The second sub-block carries ID data of four words. The third sub-block carries image data of 240 words, and the fourth sub-block carries parity check data of four words. The data lengths are given merely as an example.
In the case of digital video data, the ID data includes, for example, a specific horizontal scan line. Therefore, the image data following the ID data will be used for filling the horizontal line identified by the ID data. The parity check data includes the parity information required for error correction of the ID data and/or any other data in each block.
During the reproducing operation, the sync data is first detected, and then the ID data is read out all or partially. The read ID data is used to define an address in a memory for storing image data. Then, the image data is read out and stored in the memory at a particular area identified by the address formed by the detected ID data.
According to the prior art digital data processor as described above, when there is an error in the detected ID data, the ID data will designate wrong area in the memory. Thus, the image data following the ID data will be stored in the wrong area.
The digital VCRs available at present are mostly for business use or for professional use and, therefore, the digital VCR is equipped with a high grade arrangement which rarely produces error. Therefore, even if an error is produced in the ID data, such an error can be easily corrected by the known error correction system, one of which is the parity check system.
However, the digital VCR for the private, use or home use as will be released in the market in the near future requires a high density recording system so as to enable long VCR recording time. Therefore, the rate of generation of error becomes great, resulting in serious defects, particularly when the error occurs in the ID data, as explained below.
For example, when an error occurs in the ID data that can not be corrected by the correction system, the address defined by such ID data will provide a wrong address. Thus, the image data following the ID data will be stored in a wrong area in the memory. In other words, because the data is not written to the correct memory address, a data regenerator according to the prior art results in a block error. Moreover, this error cannot be corrected with the parity information. For example, when the ID data which should represent a location A but erroneously represents a location B, the image data will not be written to the memory area corresponding to location A, and the contents of that memory area will not be renewed properly.
When the image data is then read from memory, the non-renewed image data, i.e., the old image data which was stored in the previous loading cycle, is obtained as the data from location A, but this data differs from what the data at A should actually be. Moreover, because the data parity information also refers to this non-renewed data, it is not possible to determine whether or not the data read was the non-renewed data.
The prior art digital data processor is thus not able to detect errors resulting from various causes using the parity information in the data block itself.